1. Field of the Invention
The present invention relates to optical information recording. More particularly, the invention relates to an optical information-recording medium (e.g., an optical disk) capable of recording, reproduction, and erasing of information by irradiating a light beam, and an optical information recording/reproducing method using the medium.
2. Description of the Related Art
Optical disk recording with laser light is capable of not only recording a large amount of information but also noncontact, high-speed access and therefore, it has been practically applied to mass-storage memory devices and systems.
Optical disks are divided into some types; “Read-Only” type known as the compact disk and laser disk, the “Write-Once” type writable by the user only once, and “Rewritable” type rewritable by the user repetitively. The “Write-Once” and “Rewritable” types are used for external memory devices of computers or memory systems for recording document and/or image files.
With conventional optical disks, the reproduction signal is detected or generated from a laser beam reflected and modulated by the optical disk. For example, with the Read-Only” type optical disk, the change of amount of the reflected laser beam, which is generated by the pits on the disk, is used to derive the reproduction signal. With the “Write-Once” type optical disk, pit formation or local phase change on the disk, which is caused by irradiation of a writing laser beam, is utilized for the same purpose.
With the magneto-optical (MO) disk, which is one type of the “Rewritable” disks, the state of magnetization of the recording layer is derived from the change of polarization plane using the magneto-optical effect of the recording layer, forming the reproduction signal. With the phase-change type optical disk, which is another type of the “Rewritable” disks, phase change in the small areas of the disk caused by irradiation of a laser beam is utilized for the same purpose. This is the same as the “Write-Once” type optical disk.
Conventional optical disks comprise spiral grooves formed as the tracking guide on a transparent resin or glass substrate at a pitch of 0.74 μm to 1.6 μm. A laser beam, which is irradiated to the disk to record or reproduce the information, is focused and relatively moved along the grooves. Typically, each track in a cycle is divided into several tens of sectors and then, “preformatting pits” are formed or marked at the head of each sector in advance to record the track address, the sector address, and the synchronization signal. As the recording tracks, the grooves or the lands existing between the adjoining grooves are used. If the grooves are used for recording, it is termed the “in-groove recording”, in which the preformatting pits are formed in the grooves. If the lands are used for recording, it is termed the “on-land recording”, in which the preformatting pits are formed on the lands.
To increase the recording density of optical disks, it is effective to record the information both in the grooves and on the lands, which is termed the “land & groove recording”. This was reported by K. kayanuma et al., in the paper SPIE Proceedings, Vol. 1316, Optical Data Storage, 1990, pp. 35–39, entitled “High Track Density Magneto-Optical Recording Using a Crosstalk Canceler”. The recent “DVD-RAM” type optical disks have employed the “land & groove recording”.
As explained above, each of the circular tracks is divided into sectors, in which the track address, the sector address, and the synchronization signal are recorded by the preformatting pits. The preformatting data occupy approximately 20% of the maximum recordable amount of the disk and thus, it may be said that the preformatting data limits the available capacity of the disk. According to rough calculation of the so-called “preformatting efficiency”, it is approximately 80% for the DVD-RAMs. Since the VFO signal and the SYNC signal for synchronization in the recording or reproduction operation occupy 60% to 70% of the preformatting data, the preformatting efficiency can be improved if the synchronization signal can be derived from some data other than the preformatting data.
As one of the techniques to raise the preformatting efficiency, the “groove wobbling” method has been developed and used practically, in which the grooves are wobbled at a specific low frequency (i.e., the wobbling frequency) to record the track address information and the synchronization signal. This method has already been applied to the CD-R, CD-RW, and DVD-RW types of optical disks. For example, the CD-R type includes the wobbled grooves with the basic wobbling frequency of 22.05 kHz. The DVD-R type includes the wobbled grooves with the wobbling frequency of 140 kHz.
The “groove wobbling” method has ever been applied to only the in-groove recording, because both of the grooves and lands are difficult to be wobbled at different timing. Moreover, this method has a disadvantage that the wobbled grooves need to be formed by wobbling an optical exposure beam at high accuracy in the mastering process to produce the master disk. This method has another disadvantage that the wobbling signal itself is likely to be affected by the recording marks and thus, the wobbling signal is difficult to be detected correctly.